1. Field of the Invention
The present invention relates to a recording apparatus, in particular, to a heat transfer recording apparatus using an ink film.
2. Description of the Related Art
A heat transfer recording apparatus such as a printer comprises a platen roller and a thermal head that can be arbitrarily pressed against the platen roller. The recording paper is transferred together with the ink film between the platen roller and the thermal head to allow characters and/or graphic images printed thereon. The ink film has thermally fusing or sublimating type of inks coated on one side thereof. The ink is fused or sublimated to be fixed on the recording paper by means of the heat of the thermal head.
A heat transfer recording apparatus normally preheats its thermal head when forming images on recording paper. The preheating time of the thermal head customarily has been decided based on the temperature of the thermal head detected by means of a thermistor provided immediately above or near the thermal head. The thermistor is not directly detecting the actual thermal head temperature. As a result, when images are recorded on multiple sheets of recording paper successively, it causes a problem that the density of images recorded on recording paper earlier may not be the same as images recorded later because of the delayed response of the thermistor. The problem particularly comes into prominence in the case of half-tone images.
For example, if images are recorded on seven sheets of recording paper successively, the preheating time is set constant as there is no difference in the thermistor detection temperature. However, since the thermal head accumulates heat as time goes, the density of the images on the first to the third sheets are weaker relative to the images on the fourth to the seventh sheets.